Heat shield for an exhaust system of an internal combustion engine

ABSTRACT

The present invention provides a heat shield for an exhaust system of an internal combustion engine. The shield comprises three metal layers shaped to conform generally to the shape of a high temperature portion of said exhaust system; said metal layers having substantially the same shape and extending in face-to-face adjacency with one layer positioned between the other two layers; all three metal layers being substantially identical.

SCOPE OF THE INVENTION

[0001] This invention relates to a heat shield with thermal, acousticaland/or vibrational abatement properties and, in particular, to a heatshield for an exhaust system of an internal combustion engine.

BACKGROUND OF THE INVENTION

[0002] Heat shields for exhaust systems of internal combustion enginesare known, for example, as described in U.S. Pat. No. 5,590,524 to Mooreet al. issued Jan. 7, 1997, U.S. Pat. No. 6,177,157 to Cota issued Jan.23, 2001, and U.S. Pat. No. 6,231,944 to Holt issued May 15, 2001. Theseshields are useful to prevent heat transmitted from an engine's hightemperature components, such as the exhaust manifold, from reaching anddamaging adjacent non-metal components. Examples of operating apparatushaving non-metal components in need of protection include alternators,starter motors, turbo chargers, plastic storage containers for water andbrake cylinder reservoirs wiring and tubing. These shields are alsouseful to reduce the transfer of noise and vibrations coming from theengine and various components of the exhaust system, including themanifold.

[0003] It is desirable that a heat shield for exhaust systems ofinternal combustion engines to meet the following criteria:

[0004] (a) to provide thermal shielding;

[0005] (b) to abate noise;

[0006] (c) to abate vibrations;

[0007] (d) strength to resist damage;

[0008] (e) to protect the engine/manifold from mechanical damage;

[0009] (f) recyclable; and

[0010] (g) easy and inexpensive to manufacture.

[0011] Known heat shields for exhaust systems of internal combustionengines include those formed of a single metal layer. Among thedisadvantages of such shields are that they do not efficiently reducenoise, they have a tendency to vibrate, and that they are the leasteffective of all heat shield types in reducing conductive heat transfer.Known heat shields for exhaust systems of internal combustion enginesinclude those formed of two metal layers of either equal or unequalthickness. Such shields tend to be superior in terms of ability to abatetransfer of heat, noise and vibrations over shields formed of a singlemetal layer. However, the present inventor has appreciated that theability of these shields to abate transfer of heat, noise and vibrationscan be further improved.

[0012] Known heat shields for exhaust systems of internal combustionengines include those formed of two metal layers of either equal orunequal thickness, and a layer of insulating material (e.g. fiberglass,ceramic, aramid or air) sandwiched between the two metal layers. Suchshields are, for example, described in U.S. Pat. Nos. 5,590,524 and6,231,944. The present inventor has appreciated that such shields sufferfrom the disadvantages of not being recyclable, and of being relativelycostly and inconvenient to manufacture because of the process stepsrequired to include the layer of insulting material. Further, thepresent inventor has appreciated that the layer of insulating materialis susceptible to damage, which is caused by periodic heat shock andvibration loads of the environment and by the moisture it can absorb,thus resulting in the disintegration of the fibers and reducing theserviceable life of such shields.

[0013] U.S. Pat. No. 5,590,524 describes a shield comprising two metallayers which have substantially different thicknesses and a layer ofinsulating material between the two metal layers. This patent is a goodillustration of the approach that persons skilled in the art have takenin attempting to improve the thermal, acoustical and vibrationalabatement properties of such shields. Persons skilled in the art expectthat by providing layers which are different as in having substantiallydifferent thicknesses, these two layers would have mismatched resonantfrequencies resulting in more efficient damping and absorption ofacoustical and vibrational energy. Persons skilled in the art alsoexpect that providing a third layer of insulating material would improvethe damping properties of the shield by increasing the frictionresisting the relative movement between the two metal sheets. Further,persons skilled in the art also expect that a third layer of insulatingmaterial would provide more shielding to thermal transmission byincreasing the number of interface surface barriers within the shield.The present inventor has appreciated that surprisingly the use ofdifferent layers is not the best approach for producing shields withsuperior thermal, acoustical and vibrational abatement properties.

SUMMARY OF THE INVENTION

[0014] To at least partially overcome the disadvantages of previous heatshields, especially for applications where radiant heat management,damage protection, vibration control, noise emittance, recyclability,and geometrical restrictions are given higher priority than conductiveheat management, the present invention provides a heat shield withimproved acoustical and/or vibrational abatement properties. The presentinvention also provides a shield which has strength to resist damage, isrecyclable, and is relatively easy and inexpensive to manufacture.

[0015] An object of the present invention is to provide a shield withimproved thermal abatement properties compared to the previousdouble-layer metallic heat shields of identical overall thickness andcomparable metallic materials.

[0016] A further object of the present invention is to provide a shieldwith improved acoustical abatement properties compared to the previousdouble-layer metallic heat shields of identical overall thickness andcomparable metallic materials.

[0017] A further object of the present invention is to provide a shieldwith improved vibrational abatement properties.

[0018] A further object of the present invention is to provide a shieldwhich has strength to resist damage better than any previous heatshield, including the ones with a layer of insulating material.

[0019] A further object of the present invention is to provide a shieldwhich is recyclable.

[0020] A further object of the present invention is to provide a shieldwhich has a longer serviceable life due to better vibration management.

[0021] A further object of the present invention is to provide a shieldwhich has improved corrosion resistance without changing its basematerial and/or its coating.

[0022] A further object of the present invention is to provide a shieldwhich is relatively easy and inexpensive to manufacture.

[0023] Accordingly, in one aspect, the present invention provides a heatshield for an exhaust system of an internal combustion engine,comprising three metal layers shaped to conform generally to the shapeof a high temperature portion of said exhaust system; said metal layershaving substantially the same shape and extending in face-to-faceadjacency with one layer positioned between the other two layers; saidthree metal layers being substantially identical.

[0024] Preferably, said three metal layers are substantially identicalin being of substantially the same thickness and composition.

[0025] Preferably, one of said three metal layers may differ inthickness from the other two metal layers by not greater than 20%, morepreferably not greater than 15%, or 10%, or 5%.

[0026] Preferably, two of said three metal layers have an identicalthickness, and more preferably, all said three metal layers have anidentical thickness.

[0027] Preferably, each of said metal layers has a thickness of betweenabout 0.25 mm and about 0.5 mm, more preferably between about 0.30 mmand about 0.45 mm, or between about 0.35 mm and about 0.40 mm.

[0028] Preferably, each of said metal layers has a thickness of about0.34 mm.

[0029] Preferably, each of said three metal layers comprise the samebase metals; or two of said three metal layers comprise the same basemetals and the remaining layer comprises material that is an alloy ofthe material of the other two layers; or each of said three metal layerscomprises material that is an alloy of the material in at least one ofthe other two layers.

[0030] Preferably, each of said metal layers comprises materialsselected from the group consisting of aluminized steel, aluminum coatedsteel, aluminum cladded steel, and galvanized steel.

[0031] Preferably, said heat shield is manufactured by a process underwhich said metal layers are compressed together under pressure.

[0032] Preferably, each of said metal layers has a non-planar shape.

[0033] Preferably, each of said metal layers is deep drawn to a ratio ofdepth to thickness of from about 5:1 to about 100:1, more preferablyfrom about 10:1 to about 75:1, or from about 15:1 to about 50:1.

[0034] Preferably, hems are provided along at least some edges of saidheat shield to maintain said metal layers nested together.

[0035] Preferably, the exterior surface of said shield is coated with acoating effective to provide corrosion-resistant protection to saidshield.

[0036] Preferably, the exterior surface of said shield is coated with acoating effective to provide heat reflection.

[0037] Preferably, said coating is high temperature resistant.

[0038] Preferably, said high temperature portion of said exhaust systemis an exhaust manifold.

[0039] Preferably, said high temperature portion of said exhaust systemis selected from the group consisting of a catalytic converter, amuffler, and an exhaust pipe.

[0040] Preferably, the shield is spaced away from the exhaust system byan air gap, with preferably, a significant portion of said air gap beingbetween about 1 mm and about 30 mm, more preferably between about 3 mmand about 15 mm wide.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Further aspects and advantages will become apparent from thefollowing description taken together with the accompanying drawings inwhich:

[0042]FIG. 1 is a perspective view of a shield in accordance with apreferred embodiment of the present invention;

[0043]FIG. 2 is an inside view of the shield shown in FIG. 1;

[0044]FIG. 3 is an exploded cross-sectional view of the portionidentified as 12 in FIG. 1; and

[0045]FIG. 4 is an enlarged view of the portion identified as 20 in FIG.2 illustrating the structural detail at peripheral edge portions of theshield where a hem is formed.

[0046] Throughout all the drawings and the disclosure, similar parts areindicated by the same reference numerals.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0047] Reference is made to FIGS. 1 to 4 which show a preferredembodiment of the present invention.

[0048] As illustrated in FIG. 1, the present invention is a heat shield10. FIG. 3 illustrates an exploded cross-sectional view of the portionidentified as 12 in FIG. 1. As shown in FIG. 3, the shield 10 comprisesthree metal layers: an inner metal layer 14, a middle metal layer 16,and an outer metal layer 18. All three metal layers 14, 16 and 18 of thepreferred embodiment are identical in being of identical thickness andcomposition.

[0049] In the preferred embodiment, each of the three metal layers 14,16 and 18 has a thickness of between about 0.25 mm to 0.50 mm. The totalthickness of the three metal layers 14, 16 and 18 together is betweenabout 0.75 mm and 1.5 mm.

[0050] The shield 10 must generally be capable of surviving exposure toextreme temperature conditions caused by heat transmitted from hightemperature portions of an exhaust system. For example, shield 10 shownin FIGS. 1 to 4 is intended to be used with an exhaust manifold of aninternal combustion engine. An exhaust manifold directly receivesexhaust gases, for example at temperatures of about 1550 degrees F.,from the engine causing the exterior surface of the exhaust manifold toreach high temperatures, for example of about 1400 degrees F. and theshield 10 to reach temperatures in the range of about 1000 degrees F. Inpractice, the inner metal layer 14 generally does not exceed 1000degrees F. to 1200 degrees F. because it is spaced apart from theexhaust manifold by an air gap. Therefore, the shield 10 comprisesmaterial that can withstand a temperature of 1000 degrees F., and morepreferably 1200 degrees F. without significant degradation.

[0051] In the preferred embodiment, all three metal layers 14, 16 and 18have identical compositions in that they comprise the same base metals.This ensures similar thermal expansion rate in order to avoid buildingup frictional and compression stress among layers if exposed to heat.Specifically, the three metal layers 14, 16 and 18 of the preferredembodiment are all made from aluminized steel.

[0052] Generally, aluminized steel is produced by contacting liquidaluminum with a solid steel surface such as a steel sheet. For example,a steel sheet may be dipped in an aluminum bath. Alternatively, it isbelieved that vacuum deposition aluminum-coated steel may be used.Vacuum deposition aluminum-coated steel is produced by a process alsoreferred to as vacuum metalizing or aluminum vapor deposition, wherealuminum is vaporized, typically by applying an electric arc current toaluminum wire, and the vaporized aluminum is deposited as a thin coat orfilm on a relatively cool sheet steel substrate in close proximity, in avacuum environment. In the preferred embodiment, the steel is coatedwith a thin coating or film of aluminum on both sides of each metallayer.

[0053] To manufacture a heat shield in accordance with the preferredembodiment, blanks, consisting of the three metal layers 14, 16 and 18are obtained from a supply of aluminized steel. The three layers 14, 16and 18 are positioned relative to one another such that they are inface-to-face adjacency. Preferably, the three layers 14, 16 and 18 aremechanically secured to maintain a unitary assembly by means such as,but not limited to, tabs, hems, rivets or welding along scrap edgeportions. The inner metal layer 14, middle metal layer 16 and outermetal layer 18 are then compressed together between two dies and formedinto the desired shape in one or several forming stages using an amountof pressure of preferably from about 1200 psi to about 1400 psi.Consequently, all three layers 14, 16 and 18 have the same shape andextend in face-to-face adjacency.

[0054] In the preferred embodiment, the shield 10 is to be used with anexhaust manifold of an internal combustion engine. Therefore, the shield10 is shaped to conform generally to the shape of an exhaust manifold ofan internal combustion engine as shown in FIGS. 1 and 2.

[0055] Deep drawing techniques are used in the shaping operation toprevent unwanted folds and wrinkles from developing in the metal layers14, 16 and 18. The inventor has surprisingly and unexpectedly found thatit is possible to effectively deep draw the three metal layers 14, 16and 18 together. The inventor has also found that, by using metal layersof the same thickness and composition, it is easier to deep draw andavoid folds and wrinkles than with metal layers of different thicknessand composition. As shown in FIG. 2, the preferred embodiment is deepdrawn to a ratio of depth to thickness of from about 15:1, at D1, toabout 50:1, at D2.

[0056] As illustrated in FIG. 2, the edge portions of the shield 10 areprovided with hems 22 which maintain the three metal layers 14, 16 and18 nested together. FIG. 4 is an enlarged view of the portion identifiedas 20 in FIG. 2 illustrating the structural detail at an edge portion ofthe shield 10 where a hem 22 is formed. The three metal layers 14, 16and 18 of the preferred embodiment are nested together such that theperipheral edges of each of the metal layers are conterminous. The innermetal layer 14 is bent back upon itself at 24 to form a reverse bend andextends to a free end at 26. Similarly, the middle metal layer 16 isbent back upon itself at 28 and extends to a free end at 30. Finally,the outer metal layer 18 is bent back upon itself at 32 and extends to afree end at 34.

[0057] To help minimize the transmission of thermal and vibrationalenergy from the high temperature portion of the exhaust system to theshield 10, there is minimal physical contact between them. Preferably,the only points of physical contact are bolts which fix the shield 10 inrelation to the high temperature portion of the exhaust system such thatan air gap is provided. As shown in FIGS. 1 and 2, holes 24 are providedat various points in the preferred embodiment for use with such bolts.The width of the air gap varies due to manufacturing considerations.Preferably, the air gap is about 1 mm to 30 mm wide, and morepreferably, 3 mm to 15 mm wide, or 6 mm to 12 mm wide.

[0058] Alternative Embodiments

[0059] In alternative embodiments to the preferred embodiment describedabove, each of the three metal layers 14, 16 and 18 has substantiallythe same thickness in that one of the three metal layers may differ inthickness from the other two metal layers by not greater than 20%. Morepreferably, one of the three metal layers may differ in thickness fromthe other two metal layers by not greater than 15%, or not greater than10%, or not greater than 5%. Preferably, at least two of the three metallayers have an identical thickness.

[0060] Preferably, each of the three metal layers 14, 16 and 18 has athickness of between about 0.25 mm and about 0.5 mm. More preferably,each of the three metal layers 14, 16 and 18 has a thickness of betweenabout 0.30 mm and about 0.45 mm, still more preferably between about0.35 mm and about 0.40 mm.

[0061] The total thickness of the three metal layers 14, 16 and 18together will vary depending upon the intended application and can beselected by a person skilled in the art to meet the requirements forthermal, acoustical and/or vibrational abatement.

[0062] Preferably, each of the three metal layers 14, 16 and 18 havesubstantially the same composition in that either:

[0063] (a) all three metal layers 14, 16 and 18 comprise the same basemetals; or

[0064] (b) two metal layers comprise the same base metals and theremaining metal layer comprises material that is an alloy of thematerial of the other two layers; or

[0065] (c) each of the three metal layers 14, 16, 18 comprises materialthat is an alloy of the material in at least one of the other twolayers.

[0066] Preferably, each of the three metal layers 14, 16 and 18 isobtained from the same roll of metal sheeting.

[0067] The three metal layers 14, 16 and 18 may be made from a range ofmaterials which can be selected by a person skilled in the art.Preferably, the three metal layers 14, 16 and 18 are made fromcorrosion-resistant materials. More preferably, the three metal layers14, 16 and 18 are made from steel or aluminum, and still more preferablyfrom materials selected from the group consisting of aluminized steel,aluminum coated steel, aluminum cladded steel and galvanized steel.

[0068] The shape of the shield 10 will vary depending on the environmentin which it is intended to be used and can be selected by a personskilled in the art. The three metal layers 14, 16 and 18 are compressedtogether and formed into the desired shape using conventional tools andtechniques known to those skilled in the art. For example, stampingtechniques may be used. Consequently, all three layers 14, 16 and 18have the same shape and extend in face-to-face adjacency.

[0069] Deep drawing techniques which are known to those skilled in theart may be used in the shaping operation to prevent unwanted fold andwrinkles from developing in the metal layers 14, 16 and 18. Preferably,the shield 10 is deep drawn to a ratio of depth to thickness of fromabout 5:1 to about 100:1. More preferably, the shield 10 is deep drawnto a ratio of depth to thickness of from about 10:1 to about 75:1.

[0070] In alternative embodiments to the preferred embodiment, theshield 10 may be coated along its exterior surfaces with a hightemperature resistant paint-type coating. This coating is appliedpreferably by dipping the uncoated shield 10 into a bath of thetemperature-resistive paint coating to ensure that all exteriorsurfaces, including the edges, are fully coated. Alternatively, thecoating may be applied by spraying. After removing the shield 10 fromthe bath and allowing excess material to drip off, the coated shield 10is allowed to dry. Then, to provide a full cure of the coating, theshield 10 is baked, for example, at about 400 degrees F. for one hour.The coating material penetrates into the edge portions between the metallayers 14, 16 and 18 and forms an effective seal to prevent corrosionproducing substances from entering into the interior of the shield 10.Similarly, a full seal is formed along the edges of the hems 22. Thecured coating is about 0.001 inch thick. Two metal layers are stillconsidered to have substantially the same composition where:

[0071] (a) one metal layer has a coating while the other metal layerdoes not; and

[0072] (b) one metal layer has a coating that is different in thicknessand/or composition from the coating of the other metal layer.

[0073] The present inventor has found that, surprisingly, the thermal,acoustical and vibrational abatement properties of such shields arefurther improved by replacing the layer of insulating material fromprior art with a middle metal layer 16 which is substantially identicalto the inner metal layer 14 and the outer metal layer 18. By producing ashield 10 with three metal layers 14, 16 and 18 which are substantiallyidentical, the present invention has the following additional enhancedfeatures:

[0074] (a) The shield 10 of the present invention has a longerserviceable life than prior art shields which have a layer of insulatingmaterial. This is because the layer of insulating material is often moresusceptible to damage due to repeated heat shock, vibration and moisturethan the metal layers.

[0075] (b) The shield 10 of the present invention has better corrosionresistance due to the increased number of corrosion resistant surfacesand encapsulated mill oil films in the material sandwich.

[0076] (c) The entire shield 10 of the present invention is recyclable.In contrast, the layer of insulating material in prior art shields isoften made from materials, such as fiberglass, silica fiber, ceramicfiber, rock wool, and refractory materials in a blanket or paper formwhich are not recyclable.

[0077] (d) The shield 10 of the present invention is moreenvironmentally friendly to manufacture than prior art shields having alayer of insulating material, because there are no airborne fiberparticles present to cause respiratory hazards.

[0078] (e) The shield 10 of the present invention is moreenvironmentally friendly to operate and service than prior art shieldshaving a layer of insulating material, because there are no airbornefiber particles can be released from damaged shields.

[0079] (f) The shield 10 of the present invention is moreenvironmentally friendly to operate and service than prior art shieldshaving a layer of insulating material, because there are no chemicalbonding agents present which, when exposed to service temperatures ofthe shield, could transform and result in degasing and could alsorelease smoke.

[0080] (g) The shield 10 of the present invention is easier and lessexpensive to manufacture than prior art shields having a layer ofinsulating material. Manufacturing the above-mentioned prior art shieldsincludes the inconvenience of having to work with more than one type ofmaterial and additional process steps required to insert the layer ofinsulating material between the two metal layers.

[0081] (h) The shield 10 of the present invention is easier and lessexpensive to manufacture than prior art shields which have metal layersof different thicknesses. The metal layers 14, 16 and 18 of the presentinvention can be cut from the same coil.

[0082] The present inventor conducted extensive tests on the thermal,acoustical and vibrational abatement properties of the following typesof heat shields:

[0083] (a) Various thicknesses of a single metal layer;

[0084] (b) Various thicknesses of two metal layers which are identicalin thickness;

[0085] (c) Various thicknesses of two metal layers which differ inthickness by between 25% and 150%;

[0086] (d) Various thicknesses of two layers which differ in thicknessand having the thinner layer facing the heat source;

[0087] (e) Various thicknesses of two layers which differ in thicknessand having the thicker layer facing the heat source;

[0088] (f) Two metal layers which are identical in thickness withvarious types of insulating materials with various layer thicknessessandwiched between the two metal layers;

[0089] (g) Two metal layers which differ in thickness by greater than25% with a layer of insulating material sandwiched between the two metallayers;

[0090] (h) Three metal layers which are each different in thickness;

[0091] (i) Three metal layers which have two layers of identicalthickness as the exposed layers and a third layer of different thicknessas the encapsulated layer;

[0092] (j) Three metal layers which are identical in thickness andcomposition.

[0093] Surprisingly, the present inventor found that the heat shield ofthe present invention has improved acoustical and vibrational abatementproperties over the other metallic heat shields.

[0094] Although this disclosure has described and illustrated apreferred embodiment of the invention, it is to be understood that theinvention is not restricted to this particular embodiment. Rather, theinvention includes all embodiments which are functional or mechanicalequivalents of the specific embodiment and features that have beendescribed and illustrated herein. Many modifications and variations willnow occur to those skilled in the art. For a definition of theinvention, reference is made to the following claims.

We claim:
 1. A heat shield for an exhaust system of an internal combustion engine, comprising three metal layers shaped to conform generally to the shape of a high temperature portion of said exhaust system; said metal layers having substantially the same shape and extending in face-to-face adjacency with one layer positioned between the other two layers; said three metal layers being substantially identical.
 2. A heat shield according to claim 1, wherein said three metal layers are substantially identical in being of substantially the same thickness and composition.
 3. A heat shield according to claim 1, wherein one of said three metal layers may differ in thickness from the other two metal layers by not greater than 20%.
 4. A heat shield according to claim 1 wherein one of said three metal layers may differ in thickness from the other two metal layers by not greater than 15%.
 5. A heat shield according to claim 1, wherein one of said three metal layers may differ in thickness from the other two metal layers by not greater than 10%.
 6. A heat shield according to claim 1, wherein one of said three metal layers may differ in thickness from the other two metal layers by not greater than 5%.
 7. A heat shield according to claim 1, wherein two of the said three metal layers have an identical thickness.
 8. A heat shield according to claim 1, wherein all said three metal layers have an identical thickness.
 9. A heat shield according to claim 3, wherein each of said metal layers has a thickness of between about 0.25 mm and about 0.50 mm.
 10. A heat shield according to claim 4, wherein each of said metal layers has a thickness of between about 0.30 mm and about 0.45 mm.
 11. A heat shield according to claim 5, wherein each of said metal layers has a thickness of between about 0.35 mm and about 0.40 mm.
 12. A heat shield according to claim 8, wherein each of said metal layers has a thickness of about 0.34 mm.
 13. A heat shield according to claim 1, wherein said three metal layers together have a total thickness of between about 0.75 mm and about 1.5 mm.
 14. A heat shield according to claim 1, wherein said three metal layers together have a total thickness of between about 0.9 mm and about 1.25 mm.
 15. A heat shield according to claim 1, wherein all said three metal layers comprise the same base metals.
 16. A heat shield according to claim 1, wherein two of said three metal layers comprise the same base metals and the remaining metal layer comprises material that is an alloy of the material of the other two layers.
 17. A heat shield according to claim 1, wherein each of said three metal layers comprises material that is an alloy of the material in at least one of the other two layers.
 18. A heat shield according to claim 1, wherein each of said metal layers is obtained from the same coil.
 19. A heat shield according to claim 1, wherein each of said metal layers comprise a corrosion-resistant material.
 20. A heat shield according to claim 18, wherein each of said metal layers comprises material selected from the group consisting of aluminized steel, aluminum coated steel, aluminum cladded steel and galvanized steel.
 21. A heat shield according to claim 1, wherein said heat shield is manufactured by a process under which said metal layers are compressed together under pressure.
 22. A heat shield according to claim 1, wherein each of said metal layers has a non-planar shape.
 23. A heat shield according to claim 21, wherein each of said metal layers is deep drawn to a ratio of depth to thickness of from about 5:1 to about 100:1.
 24. A heat shield according to claim 21, wherein each of said metal layers is deep drawn to a ratio of depth to thickness of from about 10:1 to about 75:1.
 25. A heat shield according to claim 21, wherein each of said metal layers is deep drawn to a ratio of depth to thickness of from about 15:1 to about 50:1.
 26. A heat shield according to claim 1, wherein hems are provided along at least some edges of said heat shield to maintain said metal layers nested together.
 27. A heat shield according to claim 1, wherein the exterior surface of said shield is coated with a coating effective to provide corrosion-resistant protection to said shield.
 28. A heat shield according to claim 26, wherein said coating is high temperature resistant.
 29. A heat shield according to claim 1, wherein said high temperature portion of said exhaust system is an exhaust manifold.
 30. A heat shield according to claim 1, wherein said high temperature portion of said exhaust system is selected from the group consisting of a catalytic converter, a muffler, and an exhaust pipe.
 31. A heat shield according to claim 1, wherein said shield is spaced away from the exhaust system by an air gap; wherein said air gap is between about 1 mm and about 30 mm wide.
 32. A heat shield according to claim 1, wherein the exterior surface of said shield is coated with a coating effective to provide heat reflection. 